Over 300 mutations in type I collagen are associated with heritable connective tissue (CT) disorders in humans, characterized by altered matrix assembly, stability, and function. Proteoglscans', (PGs) including decorin, keratocan and lumican reside on type I collagen fibrils in various tissues, and are proposed to regulate fibril assembly and lateral association. We propose that such PG-type I collagen interactions are key regulators of matrix structure in healthy tissues, and that their disruption may be the underlying mechanism of certain CT diseases. We specifically mapped the spatial relationships between ligand-binding sites and mutation positions on type I collagen (DiLullo et al., 2002, J. Biol. Chem, 277, 4223), and reported that PGs may impact upon a number of type I collagen functions. Despite this, their sites of interaction remain poorly defined. Moreover, our map revealed that some mutations for osteogenesis imperfecta and other diseases co-localize with putative PG-binding sites, as do triple helical regions that lack reported mutations, further implicating PG-collagen interactions as key regulators of matrix structure. Thus, to better define the contribution of collagen-PG interactions to healthy tissues and to CT diseases, we will: 1) Synthesize type I collagen mimetic triple helical peptides (THPs) carrying candidate PG-binding sequences, and use them to construct a collagen peptide microarray; 2) Purify type I collagen-binding PGs and screen for their binding sites in type I collagen through use of the peptide microarray, and by affinity coelectrophoresis; and 3) Generate recombinant human Ope I collagens carrying mutated PG-binding regions and assess the effect on PG-collagen interactions and collagen fibrillogenesis. This work will: 1) increase our understanding of the role of PGs in type I collagen assembly, function, and in human diseases, 2) explore the feasibility of collagen peptide microarrays for the functional screening of collagen-intcractive ligands, and 3) lead the way to developing transgenic models for probing the in vivo function of PG-type I collagen interactions.